B cell chronic lymphocytic leukemia (B-CLL) is the most common leukemia in the Western world (Rai K, Patel D: Chronic Lymphocytic Leukemia, in Hoffman R, Benz E, Shattil S, Furie B, Cohen H, Silberstein L (eds): Hematology: Basic Principles and Practice (ed 2nd). New York, Churchill Livingstone, 1995, p 1308). Around 7,500 individuals develop and 5,000 die from this disease each year (Landis S H, et al., CA Cancer J Clin 48:6, 1998). Age is an important factor, since the incidence of B-CLL increases linearly with each decade above the age of 40 (Ries L, et al: SEER cancer statistics review 1973-1991: Tables and graphs., in Ries L, et al (eds). Bethesda, NIH, 1994; Rai K R, Clin Geriatr Med 13:245, 1997). In addition, gender is relevant, since men outnumber women by an approximate 2:1 ratio (Catovsky D, et al., Br J Haematol 72:141, 1989) and may have a worse clinical outcome (Id.; Mandelli F, et al., J Clin Oncol 5:398, 1987).
Patients with B-CLL follow heterogeneous clinical courses. Some survive for prolonged periods without definitive therapy, while others die rapidly despite aggressive treatment (Rai K, Patel D: Chronic Lymphocytic Leukemia, in Hoffman R, et al. (eds): Hematology: Basic Principles and Practice (ed 2nd). New York, Churchill Livingstone, 1995, p 1308; Zwiebel J A, Cheson B D, Semin Oncol 25:42, 1998). While various staging systems, most notably the Rai and Binet staging systems, have been developed to address this clinical heterogeneity (Rai K R, et al., Blood 46, 219, 1975; Binet J L, et al., Cancer 48:198, 1981; and Rai K: A critical analysis of staging in CLL, in Gail R, Rai K (eds): Chronic Lymphocytic Leukemia. Recent Progress and Future Directions. New York, Alan R Liss, 1987, p 253), they cannot accurately predict whether an early or intermediate stage patient will experience an indolent or aggressive course of disease. Specifically, since these systems consider gross manifestations of the disease, including the level of blood and marrow lymphocyte counts, the size and distribution of the lymph nodes, the spleen size, the degree of anemia and the patient's blood platelet count, they can only identify patients with poor prognostic outcome when the disease has progressed to a more advanced state.
At the present time, there is no known treatment for B-CLL which has been shown to definitively increase life expectancy. Consequently, only patients classified in the advanced stages of B-CLL have been considered for aggressive treatment such as chemotherapy, radiation therapy, surgery, immunotherapy or transplantation. These treatments may exact a severe physical and emotional toll on the patient without necessarily improving outcome; in some instances, B-CLL patients may even succumb from the rigors of treatment rather than from the effects of B-CLL. Patients classified in the early stages of B-CLL, who may be in better physical condition to receive more aggressive or experimental treatment, generally receive no treatment as long as the condition remains stable. This is for two reasons. First, currently available therapies do not extend life span. Second, there are currently no reliable indicators of which early stage patients will do well and which will do poorly. Further, the unpredictable course of the disease can make interpreting the results of clinical trials difficult, as some early stage patients will follow an indolent course even without the benefit of treatment.
Such drawbacks have led researchers to develop adjuvant prognostic criteria to be used in conjunction with the Rai and Binet staging systems, including several parameters such as lymphocyte doubling time (Montserrat E, et al., Br J Haematol 62:567, 1986), circulating levels of β2-microglobulin (Di Giovanni S, et al., Acta Haematol 81:181, 1989; Keating M J, et al., Blood 86:606A, 1995 (Abstract)), circulating levels of soluble CD23 (Sarfati M, et al., Blood 88:4259, 1996), serum thymidine kinase levels (Kallander C F, et al., Cancer 54:2450, 1984; Hallek M, et al., Blood 93:1732, 1999), bone marrow histology (Rozman C, et al., Blood 64:642, 1984), and cytogenetic abnormalities (Juliusson G, et al., N Engl J Med 323:720, 1990).
An accurate prognostic indicator for B-CLL not related to the symptoms of advanced disease would be desirable in the treatment and case management of B-CLL patients. Specifically, a prognostic indicator that could be evaluated at the cellular level at the earliest stages of the disease (before onset of thrombocytopenia, anemia, spleen and liver enlargement, etc.) would help physicians identify which patients would progress to a more advanced state of the disease and allow the option of more aggressive or experimental treatment at a much earlier stage. Additionally, clinical trials of new drugs or experimental therapies could be directed to patients depending upon their prognostic outlook, thereby allowing for more relevant results in clinical trials. Ideally, the expression of such a prognostic indicator would remain constant over the course of disease.
B-CLL is characterized by the clonal accumulation of CD5+ cells (Caligaris-Cappio, et al., J Exp Med 155:623-8, 1982). Although these cells originally were considered antigen inexperienced “virgin” lymphocytes, recent data indicate that at least half of these cases represent expansions of previously-triggered, post germinal center “memory” B cells (Schroeder and Dighiero, Immunol Today 15:288-294, 1994; Fais, et al., J Clin Invest 102:1515-1525, 1998). This conclusion is based on the presence of significant numbers of somatic mutations in the immunoglobulin (Ig) heavy (H) chain variable region (V) genes. In a study of 83 (64 IgM+ and 19 non-IgM+) B-CLL cases, the inventor and colleagues found significant numbers of VH mutations in approximately 50% of the IgM+ and 75% of the non-IgM+ (IgG and IgA) cases (Fais, et al, supra, 1998). Taken together with newer studies undertaken by the inventor and colleagues, VH and VL sequencing data suggest that approximately 60% of B-CLL cases can be considered to be derived from post-germinal center (GC) memory B-cells. Thus, the inventor hypothesized that B-CLL cases can be divided into two categories, namely cells clonally derived from post-germinal center memory B-cells (hereinafter referred to as “post-GC B cells”) and pre-germinal center B cells (hereinafter referred to as “pre-GC B cells”), some of which may be antigen inexperienced “virgin” lymphocytes or activated B cells that were transformed without entering a germinal center, and these categories may be relevant to prognosis.
The expression of specific cell surface markers distinguishes subsets of normal human B cells that differ in differentiation and activation stages and in biologic properties (Clark and Lane, Ann Rev Immunol 9:97-127, 1991). In particular, analyses of CD38 and IgD expression have been especially useful in distinguishing B-cells at various stages of differentiation from naive through memory cells (Pascual, et al., J Exp Med 180:329-339, 1994; Zupo, et al., Blood, 88:1365-1374, 1996).
Accordingly, the inventor sought to determine whether the distinctions based upon surface membrane phenotype of B-CLL cells (CD38+ or CD38−) or Ig V gene mutation status might predict different clinical courses and outcomes for B-CLL patients notwithstanding similar staging of these patients using conventional staging methods. Undertaking the experiments described herein, the inventor has discovered a strong correlation between CD38 expression and Ig V gene mutation, and a strong independent correlation between each of CD38 expression and IgV gene mutation and patient prognosis. Since CD38 expression in a subject's B-CLL cells may be easily and relatively inexpensively determined through various methods known and commonly used in the art, CD38 expression in particular may be a valuable prognostic indicator in B-CLL cases and should aid in the management of B-CLL patients.